1. Field of the Invention
The present invention relates to a digital cordless telephone system, and more particularly to technique for sending a broadcast voice announcement from a base station of a CT-2 cordless telephone.
2. Description of the Related Art
Generally, a base station unit in a second generation cordless telephone system (hereinafter, this system is referred to as a "CT-2" system) sends a voice announcement to a subscriber prior to the execution of a call service for the subscriber.
In an earlier CT-2 cordless telephone system, when a link is established between the base station unit and a subscriber, the base station must send voice announcement data to the subscriber. In order to send voice announcement data, a control unit included in the base station unit reads voice stated from a memory which is included in the base station unit. The voice stated is pulse coded modulation data. The control unit then sends the pulse coded modulation data read from the memory to a switching unit. The control unit continuously executes its original operation and then executes its switching operation to send the pulse coded modulation data from the control unit to an encoder. The encoder is an adaptive differential pulse coded modulation encoder which compresses the pulse coded modulation data output from the switching unit and converts the compressed data into adaptive differential pulse coded modulation data. This data is supplied to a formatter which may be a CT-2 formatter. The formatter converts the compressed data into a CT-2 format and outputs a radio frequency signal.
When the formatter outputs the voice announcement data, the switching unit outputs an interrupt signal to the control unit. In response to the interrupt signal, the control unit stops its operation and then jumps into an interrupt routine, and thereafter, the control unit executes the above-mentioned procedure.
Although the memory and encoder are respectively a source and a destination of voice announcement pulse coded modulation data in the above-mentioned configuration, they are configured to send and receive data via the control unit and the switching unit. However, the switching unit basically has a configuration which is not required for voice announcement broadcasting but is required for a normal call service. The control unit basically has a configuration required for services other than the call service. Where the control unit is configured to execute another function associated with voice announcement broadcasting, there is a disadvantage in that the control unit is overloaded. Moreover, the memory stores pulse coded modulation data in spite of the fact that the data to be finally used for broadcasting is adaptive differential pulse coded modulation data. Since pulse coded modulation data requires more storage space than the compressed data, there is a problem in that the memory which is adapted to store voice data for voice announcement broadcasting is inefficiently used.
The following U.S. patents each disclose features in common with the present invention but do not teach or suggest the specifically recited combination of features of the present invention:
U.S. Pat. No. 5,469,491 to Morley Jr. et al., entitled Telephone Answering Service With Integrated Voice And Textual Message Storage, U.S. Pat. No. 5,329,578 to Brennan et al., entitled Personal Communication Service With Mobility Manager, U.S. Pat. No. 5,321,739 to Higashiyama, entitled Cordless Telephone Apparatus With Message Recording And Reproducing Means, and U.S. Pat. No. 5,313,515 to Allen et al., entitled Call Completion System With Message Writing Indication Upon Registration Of Mobile With Basestatuion.